Developmental Norms (also Known As Developmental Milestones)
Developmental norms (also known as developmental milestones) refer to the normal timeline of mental and physical growth and changes that occur as an entity ages. In the case of human children this refers to crawling, walking, talking, etc., any of the hundreds of large and small changes that occur between birth and adulthood. If a baby has not reached a developmental norm within a normal time frame then there is a possibility that they may have a developmental delay.
For example, if a child is not walking by the time they are 17 months old then they should be tested for any motor issues that are preventing them from reaching this developmental norm.